﻿DISTEIBUTION" 
  OF 
  FISHES 
  JORDAN" 
  

  

  373 
  

  

  grown 
  hotter 
  and 
  drier, 
  until 
  the 
  overflow 
  of 
  the 
  various 
  lakes 
  

   into 
  the 
  Columbia 
  Basin 
  through 
  the 
  Snake 
  River 
  has 
  long 
  since 
  

   ceased. 
  These 
  lakes 
  have 
  become 
  isolated 
  from 
  each 
  other, 
  and 
  

   some 
  of 
  them 
  have 
  become 
  salt 
  or 
  alkaline 
  and 
  therefore 
  unin- 
  

   habitable. 
  In 
  some 
  of 
  these 
  lakes 
  certain 
  species 
  are 
  now 
  extinct 
  

   which 
  may 
  still 
  remain 
  in 
  others. 
  In 
  some 
  cases, 
  perhaps, 
  the 
  

   differences 
  in 
  surroundings 
  may 
  have 
  caused 
  divergence 
  into 
  distinct 
  

   species 
  of 
  what 
  was 
  once 
  one 
  parent 
  stock.^ 
  The 
  suckers 
  in 
  Lake 
  

   Tahoe 
  and 
  those 
  in 
  Utah 
  Lake 
  are 
  certainly 
  now 
  different 
  from 
  

   each 
  other 
  and 
  from 
  those 
  in 
  the 
  Columbia. 
  The 
  trout 
  {Salmo 
  

  

  Fia. 
  4. 
  

  

  -Tahoe 
  Trout, 
  Salmo 
  henshaioi 
  Jordan. 
  Lake 
  Tahoe 
  ; 
  this 
  and 
  the 
  next 
  are 
  

   derived 
  from 
  SnJmio 
  clarki, 
  the 
  " 
  cut-throat 
  trout." 
  

  

  Fig. 
  5. 
  — 
  Utah 
  Trout, 
  Sahno 
  clarki 
  Utah. 
  Utali 
  Lake 
  

  

  henshaioi 
  and 
  Salmo 
  clarki 
  utah) 
  in 
  waters 
  once 
  connected 
  are 
  tangible 
  

   species, 
  while 
  the 
  whitefishes 
  {Prosopium 
  williamsoni) 
  in 
  the 
  rivers 
  

   show 
  no 
  differences 
  at 
  all. 
  The 
  differences 
  in 
  the 
  present 
  faunas 
  of 
  

   Lake 
  Tahoe 
  and 
  Utah 
  Lake 
  are 
  due 
  to 
  influences 
  which 
  have 
  acted 
  

   since 
  the 
  glacial 
  epoch, 
  when 
  the 
  whole 
  Utah 
  Basin 
  was 
  part 
  of 
  

   the 
  drainage 
  of 
  the 
  Columbia. 
  But 
  the 
  separation 
  of 
  the 
  Utah 
  

   Lake, 
  Bonneville 
  must 
  be 
  much 
  more 
  recent 
  than 
  that 
  of 
  Lake 
  

   Lahontan, 
  which 
  once 
  covered 
  much 
  of 
  Nevada. 
  

  

  s 
  A 
  most 
  striking 
  case 
  of 
  species 
  formed 
  by 
  isolation 
  is 
  found 
  in 
  the 
  three 
  California 
  

   golden 
  trout, 
  "Salmo 
  agnalonita, 
  S. 
  rooseveUi, 
  (see 
  pi. 
  1) 
  and 
  S. 
  tcJiitei.) 
  shut 
  off 
  

   centuries 
  ago 
  by 
  a 
  trap 
  dyke, 
  from 
  Kern 
  River. 
  Each 
  is 
  apparently 
  derived 
  from 
  the 
  

   Shasta 
  rainbow, 
  Salmo 
  sJiasta, 
  not 
  from 
  the 
  present 
  Kern 
  trout, 
  Salma 
  oWberii. 
  

  

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